Image formats

Characteristics

© Adolf Knoll, National Library of the Czech Republic

What a format does contain?

Information about: Resolution (vertical and horizontal) Colour depth Compression … a lot of other data to enable the correct

display or printing (ICC profiles, e.g.)

Some formats offer only selected opportunities.

Types of image formats

ISO initiatives (TIFF; JPEG, JBIG, /MPEG/)

De facto standards (PNG) Very proprietary formats (PSP, PSD,

ZMF, … - internal formats of graphical tools)

TIFF – Tagged Image File Format

ISO definition A container that can incorporate so

many parameters This may cause various problems with

reading or writing TIFF

TIFF and write/read problems

Black and White (1bit, 2 colours) Huffman RLE encoding CCITT Fax Group 3 CCITT Fax Group 4 (TIFF 4)

Colour (up to 24 bits, true colour) no compression LZW (TIFF 5) Mackintosh Packbits JPEG (TIFF 6) PNG

True Colour Black and White

Grey scale256 shades of grey

Grey scale16 shades of grey

Black and White2 colours

8 bit 4 bit 1 bit

24 bit/True colour 8 bit 4 bit

16,7 million colours 256 colours 16 colours

TIFF Fax Group 4

TIFF can also contain more images (multipage TIFF, gr. 6) in one.

BMPMicrosoft Windows Bitmap

It supports 16,7 million colours, frequently only with 256 colours

It supports RLE compression Fast reading as any other

uncompressed bitmap

Web image formats

There are 3 formats recommended by the WWW consortium for web:

GIF JPEG

PNG (latest recommendation) … and also SVG

GIFGraphic Interchange Format

256 colours - palette format each GIF has its own palette this is difficult to combine LZW compression scheme highly used on the web several modifications in the WWW environment used frequently as

the so-called transparent, interlaced, or animated GIF

Palettes of GIF images

Transparent GIF

One colour in the 256-colour palette can be indicated as transparent

Animated and Interlaced GIF

Animated GIF on web pages Interlaced GIF as many other formats

can appear successively step by step

JPEGJoint Photographic Expert Group

True colour, 24 bit Lossless or lossy compression: the

compression ratio must be tuned individually (software dependent)

Possibly progressive encoding (not recommended - read problems possible)

irreplaceable for compression of photorealistic images

PNGPortable Networks Graphic

True colour format; allows up to 48 bit encoding

PNG compression: lossless, 9 degrees Slightly more economic compression

than GIF, but more colours transparency (alpha-channel) possible,

interlaced character possible

WWW and images

3 formats are recommended by the WWW consortium:

GIF, JPEG, PNG (recently)

Other formats possible, but they require special components to be installed into web browsers (ActiveX, plug-ins).